Cookie Preservatives

I am a home baker. I love to make cookies, cakes and other such treats for my friends and family. Recently I was asked if I would be interested in making cookies for a coffee shop. My home kitchen has already been inspected and approved for a "cottage industry" bakery.

I use 100 gauge food grade plastic and a heat sealer to wrap the cookies but they are not shrink wrapped, although I do have heat gun and the plastic is heat shrinkable.

I am wondering what the best way is to keep my cookies fresh. I use oil in them instead of butter but they do contain eggs.

About how long will your average chocolate chip cookie last? Is there a preservative I can add to the dough to make them last longer?